Conventionally, as a paper container for a beverage typified by a milk carton, a paper container of a gable roof type (gable top type) has been widely used. The paper container of a gable roof type is formed of a board paper raw material having a top surface and a back surface laminated with thermoplastic resins. The paper container of a gable roof type includes four body portion panels. Edge portions of the paper container of a gable roof type are bonded with each other through a longitudinal-direction seal-panel, and thus a cylindrical (tubular) body portion having a square section is formed. Upper ends of the body portion panels are continuously provided with a pair of gable roof-forming panels and a pair of gable wall-forming panels. The pair of gable roof-forming panels includes exterior top seal panels at their tops and is opposed to each other. The pair of gable wall-forming panels includes interior top seal panels at their tops and is opposed to each other. Any one of the pair of gable wall-forming panels serves as a spout and is to be opened. Between the pair of gable roof-forming panels, the pair of gable wall-forming panels is folded inside. Each of the top seal panels is heated and sealed with each other at a predetermined position so as to be hermetically sealed. In this manner, a top of the paper container of a gable roof type is formed (for example, see Patent Document 1).
In such paper container of a gable roof type, if a seal width of a top seal portion to be formed by sealing the top seal panels with each other is large, when the heated and sealed opposed surfaces of the exterior top seal panel and the interior top seal panel on a side of the gable wall-forming panel, which serves as the spout upon opening of the spout, are separated from each other, strong force is required and it is difficult to open. Thus, as one of means for facilitating opening, the top seal portion is formed to have a small seal width as long as the sealing is not deteriorated.
Further, opening of the spout in the above-mentioned paper container of a gable roof type is performed in the following manner. Specifically, the heated and sealed opposed surfaces, of the exterior top seal panel and the interior top seal panel on the side of the gable wall-forming panel, which serves as the spout as described above, are separated from each other. Then, the gable wall-forming panel folded inside between the pair of gable roof-forming panels is pulled out. After that, the pulled out gable wall-forming panel is folded back from a top-portion lateral-fold-line to the exterior, the top-portion lateral-fold-line serving as a boundary between the body portion panels continuously provided via the top-portion lateral-fold-line. In this manner, the spout is opened. However, the spout thus opened and formed exhibits a rhomboid shape elongated in a lateral direction and has a small opening area of the spout. Besides, it is difficult to pour a liquid because the liquid flows out while spreading laterally.
Then, in order to obtain a spout through which pouring is easily performed, there has been proposed the following paper container. Specifically, in the paper container, a fold line for a spout is provided to extend in a perpendicular direction from a center of the gable wall-forming panel toward a body portion panel continuously provided. The gable wall-forming panel is folded inside between a pair of gable roof-forming panels. The gable wall-forming panel is pulled out between the pair of gable roof-forming panels. The gable wall-forming panel and the body portion panel are outwardly folded along the fold line for the spout. In this manner, the spout is formed (for example, see Patent Document 2).
According to the above-mentioned paper container, the spout thus opened and formed exhibits a rhomboid shape elongated in the longitudinal direction. Upon pouring, the liquid is guided in a spout direction by a V portion formed by the gable wall-forming panel and the body portion panel which are outwardly folded. The liquid is converged at the V portion of the spout, which has a downwardly-large depth. Therefore, the liquid is smoothly poured.